Routinely, everyday, sleep and activity cycles are modulated by both what experts call the circadian rhythm and homeostatic processes. A clear understanding of what circadian rhythm and homeostatic processes actually mean can be derived of their Latin roots. “Circa diem” is the word circadian in Latin and means “one day”. Homeostasis is derived from the term homeostatic processes and means “staying the same”. More specifically, the circadian rhythm is an internal pacemaker that regulates the daily rhythms of the body and brain (Sleep 25-27). The circadian rhythm is affected most by the amount of light entered through the eyes. In coordination is what psychologists describe as the biological clock, which is a self-sustaining cycle of molecular feedback that takes 24 hours to complete (Sleep 43). Such evidence can explain why people are awake during the day when the sun is out and asleep when it becomes dark. A prime example of what happens when the clock is altered is the phenomenon of jetlag. “Jet lag is a temporary disorder that results from travel across two or more time zones” (Dawling and Mastick 163). The travel across time zones can interfere with the 24-hour light-dark cycle. Circadian rhythms can further be analyzed to describe different species use of sleep and sleep patterns.
Terrestrial mammals and birds share the same basic structures for sleep, whilst other species, such as fish and reptiles, do not. Affirmatively noted is that sleep is vital to wellness, nervous system recuperation, and normal cognitive function (Sleep and Brain Plasticity 1). Without any kind of sleep daily regulatory functions become incapable. Mammals and birds both experience the type of sleep called REM and NREM sleep. REM sleep is called “rapid eye-movement sleep” and NREM sleep is called “non rapid eye-movement sleep.” Both contribute distinct functions to sleep but the main reason mammals and birds have both types while other species may not is because of a convergent evolution hypothesis. REM and NREM sleep occur in both species because they are endothermic. Necessary thermoregulatory processes are critical to survival and REM and NREM sleep together provide temperature regulation. Some species only experience sleep with half of their brain. Fish and birds utilize unihemispheric slow-wave sleep by closing one eye and keeping one eye open. Again, an evolutionary theory explains how adaptive the behavior is because while the animal may not be fully cognizant it can still be lucid enough to defend itself from predators (Evolution of Sleep 6. Differentiating between sleep cycles can also explain specie’s unique different sleeping patterns.
Georgia State University